Circuit configuration with error detection for the actuation of power semiconductor switches and associated method

ABSTRACT

An integrated circuit configuration is provided comprising a primary side and a secondary side, for actuating power switches disposed in bridge circuit topology as well as an associated method. The primary side comprises a signal processing means and a level shifter for the potential-free actuation of the secondary side. The secondary side, in turn, comprises a signal processing means as well as a driver stage for the TOP switch. For the detection of the switched state of the TOP switch on the primary side, this side comprises a circuit section for the detection and interpretation of a current flow through a level shifter. A first lower threshold value of this current through the level shifter detected on the primary side is assigned to the not-switched-on TOP switch of the bridge circuit, and a second upper threshold value of this current through the level shifter detected on the primary side is assigned to the switched-on TOP switch of the bridge circuit.

The invention relates to a preferably integrated circuit configuration for the actuation of power switches disposed in bridge circuit topology as well as an associated method. Such bridge configurations of power switches are known as semi-, H- (two-phase) or as three-phase bridge circuits, the single phase semibridge representing the basic module of such electronic power circuits. In a semibridge circuit, two power switches, a first, so-called TOP switch, and a second, so-called BOT switch, are connected in series. As a rule, such a semibridge is connected to a direct current link. The center tapping is typically connected to a load.

When the power switches are implemented as a power semiconductor component or as a multiplicity of identical series- or parallel-connected power semiconductor components, an actuation circuit is necessary for the actuation of the power switches. Within prior art such actuation circuits are comprised of several subcircuits or function blocks. The actuation signal from a superordinate control is processed in a first subcircuit of the primary side, and, via further components, supplied to the driver circuits, the secondary sides and lastly to the control input of the particular power switch. In semibridge configurations with higher link voltages, for example greater than 50 V, the primary side, in potential/electrical terms, is isolated from the secondary side for the processing of the control signals, since the power switches, at least the TOP switch of the semibridge, during operation are not at a constant potential and consequently the isolation in terms of voltage is unavoidable. This isolation according to prior art takes place for example by means of isolating transformers, optocouplers, for example optical wave guides. This electrical isolation, is at least carried out for the TOP switch, but at higher powers also for the BOT switch due to a possible breaking of the ground reference potential during the switching.

Known are also integrated circuit configurations for power switches of the voltage classes up to 600 V or 1200 V, which forgo the use of external electrical isolation. In these monolithically integrated circuits, according to prior art, so-called level shifters are utilized, at least for the TOP switch. These electronic components and techniques for isolation consequently overcome the potential difference of the primary side with respect to the secondary side.

In this described form of the integrated circuit configuration for actuating power switches no possibility exists, at least in the simplest configuration for the secondary side of the TOP switch, for error feedback to the primary side exists.

The invention has as its aim to introduce a preferably monolithically integrated circuit configuration for power semiconductor switches in bridge configuration as well as an associated method, which permits the primary side detection of the switched state of at least one power semiconductor switch of the secondary side by means of simple and integratable means.

According to the invention this aim is attained through the measures of the characterizing clause of claim 1 and 5. Preferred embodiments are described in the dependent claims.

The inventive concept builds on a known circuit configuration for actuating power semiconductor switches in bridge topology comprised of a primary-side section (primary side) and for each power semiconductor [component] switch a secondary-side section (secondary side). The bridge circuit comprises a first, the TOP, and a second, the BOT switch. These are connected according to the prior art to a DC link. The center tapping between the TOP and the BOT switch forms the AC output of the bridge circuit. The circuit configuration for the actuation comprises on its primary side at least one signal processing means as well as at least one level shifter for the potential-free actuation of the at least one secondary side. This secondary side, in turn, comprises at least one signal processing means as well as at least one driver stage for the particular switch.

The invention introduces a preferably monolithically integrated circuit configuration for actuating power semiconductor switches, wherein for the conveyance of the switched state of the semiconductor switch from the secondary side to the primary side an already present level shifter is utilized, which, according to prior art, serves exclusively for the transmission of actuation signals from the primary side to the secondary side. On the primary side at least is disposed one circuit section for the detection and interpretation of a current flow through at least one level shifter assigned to the power semiconductor switch which is to be monitored.

The associated method serves for the primary-side detection of the switched state of a secondary-side actuated power semiconductor switch. For this purpose the current flow through the level shifter is interpreted on the primary-side. A first lower threshold value of this current through the level shifter, detected on the primary side, corresponds to a non-switched-on switch of the bridge circuit, whereas a second upper threshold value of this current through the level shifter, detected on the primary side, corresponds to a switched-on switch of the bridge circuit.

The inventive concepts will be explained in further detail in conjunction with the embodiment examples of FIGS. 1 to 6. Therein depict:

FIG. 1 a circuit configuration according to prior art,

FIG. 2 a level shifter according to prior art,

FIG. 3 a circuit configuration further developed according to the invention,

FIG. 4 the relationship between the current flow through the level shifter and the threshold value formation,

FIG. 5 a first, further developed embodiment of a level shifter for disposition in a circuit configuration according to the invention,

FIG. 6 a second, further developed embodiment of a level shifter for disposition in a circuit configuration according to the invention.

In the actuation of power semiconductor components (50, 52), such as for example IGBTs (Insulated Gate Bipolar Transistor) with antiparallel connected free-wheeling diode, in a circuit configuration in bridge topology, due to the voltage difference between superordinate control (10), for example in the form of a microcontroller (10), and the primary side (20) of the circuit configuration on the one hand, and the secondary side (30, 32) of the circuit configuration and the power semiconductor component (50, 52) on the other hand, an isolation of the potential is necessary. According to prior art, various feasibilities for potential isolation are known, for example transformers, optocouplers, optical wave guides or electronic components with appropriate electrical strength.

In the monolithic integration of primary side (20) and secondary side (30) of a circuit configuration (100) for actuating power semiconductor switches (50, 52) according to FIG. 1 level shifters (44) are frequently utilized for the transmission of control signals from the primary side (20) to the secondary side.

With said components for the potential isolation switch-on and switch-off signals can be transmitted from the primary side (20, low voltage side) to the secondary side (30, high voltage side). However, essential for the trouble-free operation of an electronic power system is the primary-side information about operating states of the secondary side (30), for example information about the concrete switched states of the TOP and of the BOT switch.

FIG. 2 shows a known topology of a monolithically integrated level shifter, here with an nMOS high-voltage transistor (430) with a blocking capacity corresponding to the maximal potential difference between primary (20) and secondary side (30). The actuation of the secondary side takes place from the primary side. As soon as the primary side (20) switches on the high-voltage transistor (430), a cross current (lq) flows between the supply voltage (Vs) of the secondary side and the ground reference potential of the primary side (20). This current flow (lq) is detected on the secondary side and converted into a signal to be processed further.

The level shifter (44) is controlled through the input signal (Sin). For this purpose, this signal is preferably preamplified and applied at the control input of a low-voltage transistor (432). As long as this low-voltage transistor (432) is open, the potential of the supply voltage (Vp) of the primary side is connected to the “source” of the high-voltage transistor (430). Since the “gate” of the high-voltage transistor (430) is also connected to the supply voltage (Vp) of the primary side (20), the entire offset voltage between primary side and secondary side falls across the high-voltage transistor (430). If the low-voltage transistor (432) is switched on, the potential at the source of the high-voltage transistor (430) falls and a cross current (lq) starts to flow. However, this current is limited by the counter-coupling resistor (424). The cross current (lq) consequently conveys the switching signal of the primary side to the secondary side thereby that here the voltage drop across the resistor (420) is interpreted. In the stationary state, in the presence of an input signal (Sin) “low”, this circuit does not consume any energy with the exception of the negligible leakage current of the high-voltage transistor (430). The signal deviation on the secondary side is limited through the Zener diode (410). Together with the resistor (424), the primary-side series connection of Zener diodes (412) protects the low-voltage transistor (432) against loading by transient overvoltages.

Due to the clamping on the secondary side and the current limitation across emitter counter coupling, the cross current (lq) during the switch-on pulse at the high-voltage transistor (430) varies with the offset voltage. The saturation behavior of the high-voltage transistor is reflected in the drain current values over the offset voltage (cf. FIG. 4).

The total voltage (cf. (Ug) in FIG. 4) results from the potential difference between the primary-side ground reference potential and the secondary-side voltage supply (Vs). Consequently, this corresponds to the sum of the offset voltage between primary and secondary side and the secondary-side operating voltage.

FIG. 3 shows a monolithically integrated circuit configuration (100) further developed according to the invention, which can, however, also be realized as a hybrid circuit configuration in the same manner. In the further development according to the invention the level shifter (44) on the primary side (20) is supplemented by a current- (46) and a voltage-acquisition means (47), as well as by a current limitation (48). Depending on the total voltage (Ug) the cross current (lq) is set up. The latter is determined via the current-acquisition means (46) and converted into a utilizable signal by means of the voltage-acquisition means (47). The current limiter (48) serves for limiting the loading of the high-voltage transistor as well as for limiting the current consumption of the level shifter (44).

The power semiconductor switches (50, 52) of the bridge configuration are utilized in switching operation, i.e. they are alternately switched on and off. The center tapping (output) of the bridge consequently has only two stationary states. If the TOP switch (50) is switched on while the BOT switch (52) switched off, the center tapping is in the proximity of the direct current link voltage; if the TOP switch (50) is switched off and the BOT switch (52) switched on, it is in the proximity of the ground reference potential. For the detection of the switched state of the TOP switch (50) therefore only the magnitude of the cross current (lq) of the level shifter (44) on the primary side (20) needs to be acquired, which is set up as a function of the magnitude of the total voltage (Ug).

When a switch-on pulse is transmitted from the primary side (20) to the secondary side (30) across the level shifter (44), the cross current (lq) depends herein on the total voltage (Ug). A switched-on TOP switch (50) is accompanied by an increase of the total voltage. Due to the described characteristic of the level shifter (44), this increase of the total voltage corresponds to an increase of the cross current lq. FIG. 4 shows this relationship schematically from the aspect of the detection circuit on the primary side. Here an increase of the cross current (lq) is determined via a second threshold value (I2) and interpreted as a consequence of the switching-on of the TOP switch. In comparison, the non-attainment (falling below) of a first threshold value (I1) is interpreted as the not-switched-on state of the TOP switch. Between the first threshold value and the second threshold value is a current difference to be defined suitable to the circuit for the correct detection of the switched states. Through the primary-side measurement of the cross current (lq) it is consequently possible to determine with certainty whether or not the secondary-side switch has been switched on as a consequence of the transmitted switch-on signal.

FIG. 5 shows a first, further developed embodiment of a level shifter (44 a) for disposition in a circuit configuration according to the invention. For simplification of the cross current (lq) detection, the threshold values can be shifted. For this purpose the secondary-side of the level shifter (44 a) is modified by a shift of the potential. The series connection of Zener diodes (414) replaces herein the individual Zener diodes (410) and the resistor (420) from FIG. 2 connected in parallel. This disposition in operation shifts the saturation value of the cross current (lq) with respect to the total voltage (Ug) and leads to a symmetric transfer characteristic. This means that the steepness of the current-voltage change in the range this side of the first threshold (I1, cf. FIG. 4) and the other side of the second threshold (I2) is shaped approximately identical. The advantage of this embodiment of the level shifter (44 a) is that even during a time period in which the assigned switch is already assumed to be switched on, a function check can consequently be performed through a further switch-on pulse. In this case also an interpretation of the cross current (lq) yields a feedback regarding the switched state of the TOP switch. With this feedback, error conditions of the secondary side, for example switch-off due to undervoltage errors, can be conveyed indirectly to the primary side and therewith to the superordinate control.

FIG. 6 shows a second, further developed embodiment of a level shifter (44 b) for the disposition in a circuit configuration according to the invention, which is based on the level shifter (44 a) according to FIG. 5. Of disadvantage in this embodiment according to FIG. 5 is that here an error transmission can exclusively [only] be initiated by the primary side, however the secondary side is not capable of actively conveying an error to the primary side. To make this possible, the series connection (414) of the Zener diodes on the secondary side is developed further such that in parallel with a plurality of these Zener diodes (414 a) a medium voltage transistor (434) is connected, which must have greater electric strength than the sum of the voltages of the Zener diodes (414 a). The remaining Zener diodes (414 b) are not affected by this modification. Of advantage herein is that, specifically in the case of monolithic integration, such medium voltage transistors (434) have lower area requirement than high-voltage transistors (432) and consequently can be integrated into the circuit configuration in technologically simpler ways, saving more space and more cost-effectively than a dedicated path for feedbacks across high-voltage transistors from the secondary side to the primary side.

In the case of a medium voltage transistor (434) actuated from the secondary side and switched off in normal operation, the behavior of the level shifter (44 b) is identical to that of FIG. 5, i.e. only in the actuation phase of the level shifter flows a significant cross current (lq). In any error case the secondary side can actively switch on this medium voltage transistor and consequently initiate a cross current flow. This flow is detected on the primary side and identified as an error signal from the secondary to the primary side. 

1-7. (canceled)
 8. A integrated circuit configuration for actuating at least a first (TOP) and a second (BOT) respective power semiconductor switches in a bridge topology, said circuit configuration comprising: a primary-side section and at least one respective secondary side section for respective power semiconductor switches in said bridge topology; said primary-side section circuitry further comprising: at least one means for signal processing and at least one assigned level shifter for enabling a potential-free actuation of said at least one secondary side; said secondary side section circuitry, further comprising: at least one means for signal processing; at least one driver stage for said respective power semiconductor switch in said bridge topology; means for detecting a switched state of said at least one power semiconductor switch, on said primary side section; and said means for detecting including at least one additional circuit section enabling a detection and an interpretation of a current flow (lq) through an assigned level shifter.
 9. A circuit configuration, according to claim 8, wherein: said at least one additional circuit section for said means for detecting includes at least one of a means for current-acquisition, a means for voltage acquisition, and a means for current-limitation.
 10. A circuit configuration, according to claim 8, wherein in circuit connection, said assigned level shifter, further comprises: one secondary-side voltage supply (Vs); at least one Zener diode; a secondary-side output (Vo); a high-voltage transistor; a primary-side voltage supply (Vp); and a low-voltage transistor.
 11. A circuit configuration, according to claim 10, wherein: said level shifter following said voltage supply on said secondary side section, following the voltage supply on this side, further comprising: at least one series connection of Zener diodes.
 12. A circuit configuration, according to claim 4, further comprising: a medium-voltage transistor disposed in parallel with at least one series connection of Zener diodes.
 13. Method for detecting a switched state of a power semiconductor switch in a circuit configuration for actuating at least a first (TOP) and a second (BOT) respective power semiconductor switches in a bridge topology, comprising the steps of: interpreting a current flow (lq) through a level shifter on a primary side section by means of at least one circuit section; said at least one circuit section being one of a means for current acquisition, means for voltage acquisition, and a means for current limitation; said step of interpreting further comprising the steps of: detecting a first lower threshold value (I1) of said current flow (lq) through said level shifter on said primary side section; said first lower threshold value (I1) being a corresponding not-switched-on state of one of said power semiconductor switches of said bridge topology; detecting a second upper threshold value (I2) of said current flow (lq) through said level shifter on said primary side section; and said second upper threshold value (I2) being a corresponding to a switched-on switch state of said one of said power semiconductor switches of said bridge topology.
 14. A method for detecting, according to claim 13, further comprising the step of: detecting said current flow (lq) through said level shifter by means of at least one means for current acquisition and at least one means for voltage-acquisition, whereby said method readily enables error detection of said power semiconductor switches.
 15. A method for detecting, according to claim 13, further comprising the step of: providing a means for current limitation on said primary side section, thereby preventing an overloading of said level shifter. 